Ultrashort wave antenna system



March 1933- K. FRITZ 2 ULTRASHORT WAVE ANTENNA SYSTEM Filed Aug. 10, 1935 FEED 1.51905 0; DIFFERENT (ENG 7/1 HIGH FREQUENCY TRfl/VSLRT/Nti APP/7 EA TUJ INVENTOR. KARL FRITZ BY m x ATTORNEY.

Patented Mar. 29, 1938 NET STAT 2,112,282 ULTRASHORT WAVE ANTENNA SYSTEM Karl Fritz, Berlin,

Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. 11., Berlin, Germany,

many

a corporation of Ger- Application August 10, 1935, Serial No. 35,595

In Germany September 3,

2 Claims.

The invention is concerned with a useful and advantageous antenna arrangement comprising reflector means which is of a nature to insure an increase energy yield (efficiency) in reception and an increase in radiated energy in transmission. The same may be used for short and ultra-short Waves, such as centimeter and decimeter waves.

Metallic reflectors or mirrors intended to insure concentration of parallel rays and paralleling of divergent rays are extensively used, though not always with the desired success. For instance, if in the focus of a paraboloid reflector i (see Fig. 1) there is mounted a receiving dipole 2, the incoming energy thus picked up will amount to only a small fraction of the aggregate radiation energy reflected from the surface of the mirror. This, in the first place, is ascribable to the fact that the wave-lengths used at the present time (even where extremely short waves of about 1 meter are dealt no with) are not negligibly small compared to the dimensions of the mirror, as is true of luminous rays and not unduly small mirrors. In other words, the laws underlying geometrical optics will hold good in this case only to a proximate degree. Above all, there exists here no pronounced focus. As a result of diffraction phenomena, even in the case of extremely precise paraboloid reflectors, thev reflected energy will fail to be concentrated in one point or focus, but rather inside a space being of finite size comparable to the length of the waves, this space to be called the focal space. In the case of spherical mirrors, there must further be considered a phenomenon known as spheric aberration, and, with oblique incidence, the phenomenon of astigmatism, and this means an additional blurring of the focus and a further enlargement of the focal space.

Fig. l is given by way of illustration and shows a known type of structure, and Figs. 2 and 3 ilustrate two embodiments of the invention.

Referring to Fig. 1, it will be noted that the focal space, i. e., the geometric locus of the points where the concentration of energy is appreciable, has been indicated by the hatched area 3. It will be understood that an exact determination of the volume of the focal space is a function. of the question as to what degree of concentration of the energy, contrasted with the maximum occurring concentration, may still be regarded as considerable or appreciable. 7

At any rate, it will be noted that a dipole 2 disposed inside what was above called the focal space will absorb only a small part of the energy contained within and permeating the said space.

However, there are other factors which affect the energy utilization, and among these may be mentioned primarily:

1. Phase differences of the potentials induced in its various parts and being due tothe finite dimensions of the radiation absorbing means;

2. Directional property of the radiation absorbing means (or of the radiator, as the case may be) and 3. Change in polarization of the rays subject to the effect of reflections. At those places where the incident wave is polarized not normal, and not parallel, to the plane of incidence, as will be seen, either the plane of polarization of the reflected wave will be turned or else elliptic polarization will be occasioned.

Now, according to this invention, the efficiency or performance of an antenna comprising a reflector or mirror may be considerably improved if the radiator or the radiation-collector means consists of an antenna system which is distributed inside the focal space, or in a cross-section thereof, say, an antenna system shaped in accordance with a beam system or some similar complex arrangement.

A system of the said sort is illustrated in Fig. 2 at 4. A plurality of dipoles associated with energy feeders are here so distributed inside a cross-section of the focal space 3 and so spaced apart that the energy traversing or permeating this space will be utilized under optimum conditions.

A further improvement is obtainable if the complex antenna is so chosen that its radiation diagram will be adapted to the mirror; in other words, that the angle which bounds or demarcates its radiation (without reflector) will be proximately equal to the angle under which the reflector is viewed from the antenna system. This is indicated in Fig. 3. In this case, the directional system consists, for instance, of a complex or a plurality of dipoles 4 and similar reflectors 5, the said complex resulting in a radiation diagram or pattern 6 the solid angle of which corresponds to the solid angle under which the mirror appears viewed from the antenna system.

In this arrangement, the auxiliary reflector mounted posteriorly of the dipoles and which otherwise must be provided with a dipole furnished with reflector means, will be found unnecessary.

In order to take into consideration the rotation of the plane of polarization or the elliptical polarization of the waves reflected from the mirror, it is recommendable and preferable to so shape the antenna system that it will be capable of simultaneously receiving (or radiating) difierently polarized waves; in fact, this condition may be secured, e. g., by the arrangement of two crossed dipoles, or dipole systems.

In order to equalize or compensate for the effects of phase differences in oscillatory state of the various dipoles or parts of the beam system, the length of the energy feeders or leads should preferably be chosen correspondingly, as is normally customary with systems of the said sort. However, the desired compensation could be secured also by disposing the antenna system not in a plane, but rather in a suitably curved surface, or else in stages or steps, and, in this instance, a correction of the diagram angle may turn out to be necessary.

What I claim is:

1. In an ultra short Wave receiving system, in combination, a reflector in the form of a surface of rotation having an enlarged focal area wherein the concentration of energy received by said reflector is appreciable, and an antenna system comprising a plurality of spaced antennae within the focal area of said reflector, and receiving apparatus coupled to said spaced antennae, said reflector being of such size and so constructed that the radiation diagram of said antennae without said reflector has an angle approximately equal to the angle under which said reflector appears as measured from said antennae to the contour of said reflector.

2. An ultra short wave system comprising a reflector in the form of a surface of rotation having an enlarged focal area, and an antenna system comprising a plurality of spaced antennae within the focal area of said reflector, and high frequency apparatus, energy leads extending from said high frequency apparatus to said antennae, said energy leads extending to different antennae differing in length to compensate for the phase differences of said antennae due to their spacing.

KARL FRITZ. 

